I want to start an etsy embroidery company and donate a percentage of each sale to helping conserve the ocean. What percentage?

That's something you are going to need to figure out.

Start by donating a percentage of profit.  That way, you know that you'll have some profit left and a won't be donating all of it.  Once you've been doing it longer enough to know what percentage of sales equals your profit, you donate anything less than that.

Since you don't know your own numbers and you're asking a bunch of clueless anonymous Yahoos to run financial statements for you you'll have no profit to give away.